Volume 17, Issue 2 (April 1995)

Modes of Failure of Fibrous Composite Materials as Affected by the Orientation-Angle of Fiber

An energy-based failure criterion has been recently developed by the authors. At any stress level, the model deals with the actual composite material as an equivalent linear elastic material. The total strain energy density of the system is considered to be composed of two parts, elastic and plastic. In this paper, the model has been used to identify the modes of failure based on the relative magnitudes of the various energy terms appearing in the failure criterion equation. Accordingly, three types of failure are anticipated: fiber failure, matrix failure (tension or compression), and matrix failure in shear. The critical fiber orientation for a given stress state can be predicted as well.

The model has been verified using available experimental data in the literature and compared with other theoretical models as well. Good agreement has been obtained in both cases.

The failure envelopes for boron-epoxy Narmco 5505 and glass-epoxy 3MXP 251S are predicted using several stress combinations and fiber orientations ranging from 0 to 90°. Seven failure envelopes are obtained, classified as A, B, C, D, E, F, and G.